Effect of Slurries and Substrate Combination Ratios on Biogas Production from Rice Husk and Cow Dung

Abstract

This work studied the effect of varying ratios of substrates on biogas production from rice husk and cow dung and was carried out using different slurry concentration of 1:4 and 1:12 solid to water ratios and monitored over 48 days. The results from daily production show that all the digesters started biogas production in day 1, with rice husk recording the highest biogas of (400 cm³), while most of the digesters recorded their highest biogas production in the early days. It was observed that rice husk stopped production in day 29 and 38 with biogas yield of 10 cm³ and 5 cm³ respectively. The weekly biogas production for the digesters in 1:4 and 1:12 ratios shows that hydrolysis of rice husk takes place faster than cow dung, were rice husk produces the highest biogas of (2190 cm³) in week 1 and rice husk plus cow dung with the highest biogas yield of (580 cm³) in week 4. It was also observed that only cow dung was producing biogas steadily at an average temperature of 35 °C. The effect of slurry concentration on the substrates used shows that; less dilute slurry is better for biogas production, D1>D4 and D2>D5 for Rice husk and cow dung respectively, 
while for the combination of rice husk and cow dung shows the reverse case D6>D3. proximate analysis shows the % moisture content for rice husk (10 %), cow dung (15 %) and %Organic matter content for rice husk (5 %), and cow dung (10 %), this indicates both samples can make a better substrate for biogas production with the trend cow dung > rice husk. From the search conducted, it may be concluded that slurry concentration plays a vital role in biogas production than substrate combination ratios with less slurry concentration showing a promising trend for optimum biogas yield as a sustainable energy sources.